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Module 10: Implementing User-defined Functions
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Overview What Is a User-defined Function? Defining Examples
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What Is a User-defined Function? Scalar Functions (do not reference tables) Similar to a built-in function Multi-Statement Table-valued Functions Content like a stored procedure Referenced like a view In-Line Table-valued Functions Similar to a view with parameters Returns a table as the result of single SELECT statement
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Defining User-defined Functions Creating Creating with Schema Binding Setting Permissions Altering and Dropping
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Creating a User-defined Function USE Northwind CREATE FUNCTION fn_NewRegion (@myinput nvarchar(30)) RETURNS nvarchar(30) BEGIN IF @myinput IS NULL SET @myinput = 'Not Applicable' RETURN @myinput END USE Northwind CREATE FUNCTION fn_NewRegion (@myinput nvarchar(30)) RETURNS nvarchar(30) BEGIN IF @myinput IS NULL SET @myinput = 'Not Applicable' RETURN @myinput END Creating a Function Restrictions on Functions CREATE FUNCTION dbo.fn_NewRegion CREATE FUNCTION dbo.fn_NewRegion
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Creating a Function with Schema Binding Referenced User-defined Functions and Views Are Also Schema Bound Objects Are Not Referenced with a Two-Part Name Function and Objects Are All in the Same Database Have Reference Permission on Required Objects
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Setting Permissions for User-defined Functions Need CREATE FUNCTION Permission Need EXECUTE Permission Need REFERENCE Permission on Cited Tables, Views, or Functions Must Own the Function to Use in CREATE or ALTER TABLE Statement
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Altering and Dropping User-defined Functions Altering Functions Retains assigned permissions Causes the new function definition to replace existing definition Dropping Functions ALTER FUNCTION dbo.fn_NewRegion ALTER FUNCTION dbo.fn_NewRegion DROP FUNCTION dbo.fn_NewRegion
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Examples of User-defined Functions Scalar User-defined Function UsageExample Multi-Statement Table-valued Function UsageExample In-Line Table-valued Function UsageExample
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Using a Scalar User-defined Function RETURNS Clause Specifies Data Type Function Is Defined Within a BEGIN and END Block Return Type Is Any Data Type Except text, ntext, image, cursor, or timestamp
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Example of a Scalar User-defined Function USE Northwind CREATE FUNCTION fn_DateFormat (@indate datetime, @separator char(1)) RETURNS Nchar(20) AS BEGIN RETURN CONVERT(Nvarchar(20), datepart(mm,@indate)) + @separator + CONVERT(Nvarchar(20), datepart(dd, @indate)) + @separator + CONVERT(Nvarchar(20), datepart(yy, @indate)) END USE Northwind CREATE FUNCTION fn_DateFormat (@indate datetime, @separator char(1)) RETURNS Nchar(20) AS BEGIN RETURN CONVERT(Nvarchar(20), datepart(mm,@indate)) + @separator + CONVERT(Nvarchar(20), datepart(dd, @indate)) + @separator + CONVERT(Nvarchar(20), datepart(yy, @indate)) END SELECT dbo.fn_DateFormat(GETDATE(), ':') Creating the Function Calling the Function
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Using a Multi-Statement Table-valued Function BEGIN and END Enclose Multiple Statements RETURNS Clause Specifies table Data Type RETURNS Clause Names and Defines the Table
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Example of a Multi-Statement Table-valued Function Creating the Function Calling the Function USE Northwind GO CREATE FUNCTION fn_Employees (@length nvarchar(9)) RETURNS @fn_Employees table (EmployeeID int PRIMARY KEY NOT NULL, [Employee Name] nvarchar(61) NOT NULL) AS BEGIN IF @length = 'ShortName' INSERT @fn_Employees SELECT EmployeeID, LastName FROM Employees ELSE IF @length = 'LongName' INSERT @fn_Employees SELECT EmployeeID, (FirstName + ' ' + LastName) FROM Employees RETURN END USE Northwind GO CREATE FUNCTION fn_Employees (@length nvarchar(9)) RETURNS @fn_Employees table (EmployeeID int PRIMARY KEY NOT NULL, [Employee Name] nvarchar(61) NOT NULL) AS BEGIN IF @length = 'ShortName' INSERT @fn_Employees SELECT EmployeeID, LastName FROM Employees ELSE IF @length = 'LongName' INSERT @fn_Employees SELECT EmployeeID, (FirstName + ' ' + LastName) FROM Employees RETURN END SELECT * FROM dbo.fn_Employees('LongName') Or SELECT * FROM dbo.fn_Employees('ShortName') SELECT * FROM dbo.fn_Employees('LongName') Or SELECT * FROM dbo.fn_Employees('ShortName')
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Using an In-Line Table-valued Function Content of the Function Is a SELECT Statement Do Not Use BEGIN and END RETURN Specifies table as the Data Type Format Is Defined by the Result Set
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Example of an In-Line Table-valued Function Creating the Function Calling the Function Using a Parameter USE Northwind GO CREATE FUNCTION fn_CustomerNamesInRegion ( @RegionParameter nvarchar(30) ) RETURNS table AS RETURN ( SELECT CustomerID, CompanyName FROM Northwind.dbo.Customers WHERE Region = @RegionParameter ) USE Northwind GO CREATE FUNCTION fn_CustomerNamesInRegion ( @RegionParameter nvarchar(30) ) RETURNS table AS RETURN ( SELECT CustomerID, CompanyName FROM Northwind.dbo.Customers WHERE Region = @RegionParameter ) SELECT * FROM fn_CustomerNamesInRegion('WA')
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Recommended Practices Use Multi-Statement Functions Instead of Stored Procedures That Return Tables Use Multi-Statement Functions Instead of Stored Procedures That Return Tables Use In-Line Functions to Filter Indexed Views Use Complex Scalar Functions on Small Result Sets Use In-Line Functions to Create Parameterized Views
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Review What Is a User-defined Function? Defining Examples
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